The present invention relates to a vibration isolator which includes an inner cylindrical metal member, an outer cylindrical metal member located outside the inner cylindrical metal member in a radial direction, and a rubber elastic member interposed between the inner and outer cylindrical metal members so as to elastically connect between these metal members, and is supported by a support metal member forced and fixed into an axial hole of the inner cylindrical metal member.
Conventionally, the background art teaches a vibration isolator with a differential mount as shown in FIG. 11 and FIG. 12. This vibration isolator includes: an inner cylindrical metal member 1; a rubber elastic member 2 which is bonded to an outer circumferential surface of the inner cylindrical metal member 1 by vulcanization adhesion and has a cross section of approximately cross shape; an outer cylindrical metal member 3 which is fitted and fixed outside the rubber elastic member 2; and a cantilever support metal member 4 which is forced and fixed into an axial hole of the inner cylindrical metal member 1 and has a bolt part projecting into the outside at its one end side. By forcing the support metal member 4 into the axial hole of the inner cylindrical metal member 1, the support metal member 4 is firmly fixed to the inner cylindrical metal member 1, and its drawing (removing) force is the substantially same as a press-fit force. The outer cylindrical metal member 3 is forced and fixed into a support bracket of a differential gear case (not shown). The bolt part of the support metal member 4 is inserted into a mounting hole of a body sub-frame (not shown), and further, a nut is screwed into the distal end portion of the support metal member 4, and thereby, the support metal member 4 is supported to the body sub-frame like a cantilever support.
In the above vibration isolator, in order to suppress a vibration amplitude to a proper amplitude with respect to an excessive vibration input, as seen from a comparative example shown in FIG. 9 and FIG. 10, a request has been made to attach a stopper member 5 which extends to a vibration input direction at the axial center of the inner cylindrical metal member 1. The stopper member may be made of a resin or metal, and in light of reducing weight of the vibration isolator, a resin-made stopper member is preferred.
However, the force fit of the support metal member into the axial hole of the inner cylindrical metal member is carried out after the stopper member is fixed to the inner cylindrical metal member; for this reason, the inner cylindrical metal member is enlarged in its diameter. As a result, a great pushing pressure is applied to the stopper member. In the case where the resin stopper member is employed, the resin is brittle to a tensile stress; for this reason, a strain applied to the stopper member becomes great by the aforesaid enlargement of the diameter of the inner cylindrical metal member by a force fit operation. As a result, there is a problem that the stopper member is insufficient in its strength and is lack of a durability. Moreover, in the case of using a metallic stopper member which is formed integrally with the inner cylindrical metal member by forging, or formed by forging or the like and is forced into an inner cylindrical metal member, when the support metal member is forced into the inner cylindrical metal member, a portion having no stopper of the inner cylindrical metal member is elastically deformed; on the other hand, a portion having a stopper is plastically deformed because a resistance in force fit becomes great. As described above, there exists a portion which is plastically deformed; for this reason, the drawing force of the support metal member is reduced to about a half of press-fit force. As a result, this is a factor of losing a function of stably supporting the inner cylindrical metal member of the support metal member.
Moreover, as a vibration isolator having the same structure, there is a vibration isolator including a rubber elastic member formed between the inner and outer cylindrical metal members by vulcanization molding. The rubber elastic member is provided with a so-called ring-like hollow recess portion which extends by a predetermined dimension toward an axial direction along the vicinity of an inner wall of the outer cylindrical metal member from both end of the axial direction and over the entire circumferential direction. Likewise, in the vibration isolator, in order to suppress a vibration amplitude to a proper amplitude with respect to an excessive vibration input, a ring-like stopper member extending in a diameter direction is mounted to the inner cylindrical metal member at both end sides of the axial direction; however, in this case, the same problem as above arises by the force fit of the support metal member into the axial hole of the inner cylindrical metal member.
The present invention has been made to solve the aforesaid problem. It is, therefore, an object of the present invention to provide a vibration isolator which can prevent a damage of a stopper member by a force fit of a support metal member into an axial hole of an inner cylindrical metal member fixing the stopper member at its outer circumferential surface, and can secure a proper drawing force of the support metal member.
In order to achieve the above object, the present invention provides a vibration isolator including: an inner cylindrical metal member formed in a manner that axial one portion of a metallic pipe is coaxially bulged into a radial direction to axial another portion, and one portion is a large-diameter portion whose inner and outer diameters are slightly larger than inner and outer diameters of another portion; a stopper member fixed to an outer peripheral surface of the large-diameter portion and projecting into a radial direction; an outer cylindrical metal member arranged outside the inner cylindrical metal member including the stopper member in a radial direction; and a rubber elastic member interposed between the inner cylindrical metal member and the outer cylindrical metal member so as to connect elastically between inner cylindrical metal member and the outer cylindrical metal member, the vibration isolator being supported by a support metal member forced into an axial hole of the inner cylindrical metal member.
The position locating the large-diameter portion of the inner cylindrical metal member may be an axial intermediate portion. Moreover, the position locating the large-diameter portion may be axial both end side portions. A material for forming the stopper member may be a resin.
By doing so, before the support metal member is forced into the axial hole of the inner cylindrical metal member, axial one portion of the inner cylindrical metal member including a portion locating the stopper member is formed into a large-diameter portion whose inner and outer diameters are slightly larger than inner and outer diameters of another portion. Therefore, when the support metal member is forced into the axial hole of the inner cylindrical metal member, other portion excluding the large-diameter portion of the inner cylindrical metal member are slightly enlarged in its diameter; however, the large-diameter portion receives no influence by the force-fit of the support metal member.
For this reason, in the case where the stopper member is made of a resin, it is possible to secure a reliability without lowering a strength of the stopper member by the force-fit of the support metal member, and further, to maintain a drawing force of the support metal member. Moreover, in the case where the stopper member is made of metal, when the support metal member is forced into the axial hole of the inner cylindrical metal member, only small-diameter portion other than the large-diameter portion of the inner cylindrical metal member is elastically deformed, and the large-diameter portion locating the stopper member receives almost no influence; therefore, a drawing force of the support metal member can be maintained without being lowered.
A stepped portion of the large-diameter portion of the inner cylindrical metal member and other portions thereof is an inclined surface, and thereby, the inner cylindrical metal member is smoothly enlarged in its diameter. Moreover, a force-fit allowance of the support metal member and the inner cylindrical metal member is set to a range from 0.05 to 0.5 mm in a diametrical dimension, and thereby, it is possible to properly secure a drawing force of the support metal member.